1. BTI and A-BFT for EDMG AP with Multiple Antennas
Sep 2017
doc.: IEEE /XXXXr0
October 2017
BTI and A-BFT for EDMG AP with Multiple Antennas
Date:
Author:
Yanchun Li, Huawei Technologies
Yanchun Li, Huawei Technologies

2. Motivation 11ad enables BTI and A-BFT for AP with multiple antennas.
Sep 2017
doc.: IEEE /XXXXr0
October 2017
Motivation
11ad enables BTI and A-BFT for AP with multiple antennas.
However, due to limitation of single RF chain (SISO), AP is only allowed to use one antenna within each beacon interval (BI).
Sector Sweeping for multiple antennas has to span over lots of BIs.
This presentation discusses that EDMG AP with multiple antennas (multiple RF chains) can allow sector sweeping of more than one antennas in BTI and A-BFT in a BI.
Yanchun Li, Huawei Technologies
Yanchun Li, Huawei Technologies

3. Recap BTI and A-BFT for DMG AP with multiple antennas in 11ad
October 2017
Recap BTI and A-BFT for DMG AP with multiple antennas in 11ad
Beamforming in BTI
“The AP or PCP shall not change DMG antennas within a BTI. ” [1]
Beamforming in A-BFT with multiple DMG antennas
“An AP or PCP shall receive through a quasi-omni antenna pattern from a single DMG antenna throughout an A-BFT unless RXSS is used in the A-BFT” [1]
“In an A-BFT, the AP or PCP shall receive in a quasi-omni antenna pattern using the DMG antenna indicated by the value of the DMG Antenna ID subfield within the SSW field transmitted in the DMG Beacon.” [1] …
Fig.1 (Green Triangle: Active Rx Antenna
Gray Triangle: Inactive Rx Antenna)
Yanchun Li, Huawei Technologies

4. Recap BTI and A-BFT for DMG AP with multiple antennas in 11ad
October 2017
Recap BTI and A-BFT for DMG AP with multiple antennas in 11ad
“An AP or PCP with multiple DMG antennas has a regular schedule of receiving through each DMG antenna corresponding to the DMG antenna in which a DMG Beacon frame is transmitted through. The AP or PCP shall switch RX DMG antenna every l allocations, where l is the value of the N A-BFT in Ant subfield within the Beacon Interval Control field.” [1]
Yanchun Li, Huawei Technologies

5. Recap BTI and A-BFT for DMG AP with multiple antennas in 11ad
October 2017
Recap BTI and A-BFT for DMG AP with multiple antennas in 11ad
Note that if AP uses more than one antennas in BTI，a DMG AP can’t receive with these antenna simultaneous in A-BFT.
Consider a DMG AP with multiple antennas, it needs lots of Beacon Intervals to cover all these antennas.
For example, at least 4 BIs are required by AP with 4 antennas
AP rx with
AP tx with … … … …
Yanchun Li, Huawei Technologies

6. Proposed BTI and A-BFT for EDMG AP with multiple antennas
October 2017
Proposed BTI and A-BFT for EDMG AP with multiple antennas
AP can use multiple antennas in BTI and A-BFT to
Speed up SLS
Increase robustness and coverage
When AP or PCP uses more than one DMG antennas (sequentially or simultaneously) for DMG Beacon transmissions during BTI, the AP or PCP shall include these antennas for receiving in a quasi-omni antenna pattern in the corresponding A-BFT.
Yanchun Li, Huawei Technologies

7. Benefits: flexible and fast Initiator SS in BTI
October 2017
Benefits: flexible and fast Initiator SS in BTI
For EDMG AP with multiple RF chains (MIMO capability), it can use much less BIs to cover all antennas. … …
Yanchun Li, Huawei Technologies

8. Benefits: enable efficient Responder SS in A-BFT
October 2017
Benefits: enable efficient Responder SS in A-BFT
Consider a cell edge EDMG STA, it can know AP use antenna 1 and 3 in A-BFT, if it receives Beacon from antenna 1 and 3 in BTI. Its responder Sector Sweeping is more likely to be captured by AP during this A-BFT, since AP can capture this edge STA’s SSW frame from both of these antennas. … … … …
Yanchun Li, Huawei Technologies

9. Benefits: enable efficient Responder SS in A-BFT (an example)
October 2017
Benefits: enable efficient Responder SS in A-BFT (an example)
For example, an edge STA’s SSW signal may not strong enough to be received from AP’s single antenna. But it can be more easily be detect by AP when AP receives with both antenna 0 and antenna 2 in quasi-omni mode.
When this edge STA receives beacons from AP’s antenna 0 and 2 within a BTI of a BI, it can choose to transmit SSW in the A-BFT of this BI. Because this rx antenna combination is beneficial for this edge STA.
STA1
STA1
STA1
STA1
Can’t hear ant0
Ant 1 alone is not good enough.
This rx antenna combination is sufficient
Ant 2 alone is not good enough.
Can’t hear ant3 … … … …
Yanchun Li, Huawei Technologies

10. IFS for Antenna Switching in BTI
October 2017
IFS for Antenna Switching in BTI
AP can transmit via multiple RF chain in turn (alternatively). Thus, IFS between the Beacon frames transmitted by previous antenna and next one can be SBIFS.
Yanchun Li, Huawei Technologies

11. IFS for Antenna Switching in BTI (Continue)
October 2017
IFS for Antenna Switching in BTI (Continue)
The IFS does not have to be LBIFS, because AP with multiple RF chains can transmit via each RF chain in turn. Thus, when RF chain 0 transmits nth beacon and then switches its antenna, RF chain 1 can be prepared in advance and transmit n+1 th beacon only SBIFS after nth beacon’s transmission.
AP just need to trigger the transmission from RF chain 1 according its clock source (as it will trigger the transmission from old RF chain 0 when AP performs Tx beam sweeping without antenna change). And the clock source has high enough precision since “The symbol clock frequency tolerance shall be ± 20 ppm maximum.”.
So, legacy SBIFS and aSBIFSAccuracy is applied here:
“A STA shall not allow the space between frames that are defined to be separated by a SBIFS time, as measured on the medium, to vary from the nominal SBIFS value (aSBIFSTime) by more than aSBIFSAccuracy.” (aSBIFSAccuracy = [0, +0.03] μs)
Yanchun Li, Huawei Technologies

12. Low A-BFT density cases
October 2017
Low A-BFT density cases
A EDMG AP with multiple antennas can transmit beacon frames with one antenna per BTI over multiple BIs and then allocate an A-BFT. AP can receive with at least the antennas used over these BIs within A-BFT.
AP needs to notify which antennas will be used for receiving in A-BFT.
Or AP will receive with the antennas used in recent BTIs (from last A-BFT till now) by default.
STA may wait and start RSS in the A-BFT which AP receives with STA’s preferred antenna(s).
Yanchun Li, Huawei Technologies

13. Backward compatibility
October 2017
Backward compatibility
Each DMG Beacon frame contain Antenna ID in SSW field.
DMG Beacon frames are transmitted sequentially.
DMG Beacon frames can be detected sequentially at legacy STAs.
Legacy DMG STA feedbacks the sector ID + antenna ID with highest SNR in Initiator-SS (BTI) as legacy RSS behavior defined in 11ad:
“The responder shall set the Sector Select field and the DMG Antenna Select field in each transmitted SSW frame to the value of the Sector ID field and DMG Antenna ID field, respectively, of the frame received with the best quality during the ISS.”
Yanchun Li, Huawei Technologies

14. Sep 2017
doc.: IEEE /XXXXr0
October 2017
Conclusion
AP can use multiple antennas in BTI and A-BFT of a Beacon Interval. It can allow ISS in less BIs, more flexible and efficient initial sector sweeping.
Yanchun Li, Huawei Technologies
Yanchun Li, Huawei Technologies

15. Straw Poll Do you agree:
October 2017
Straw Poll
Do you agree:
to allow an EDMG AP to use multiple antennas in BTI and A-BFT of a Beacon Interval by inserting the text in ‘ ay-BTI-and-A-BFT-for-EDMG-AP-with-Multiple-Antennas-text.docx’ into D0.5?
Yanchun Li, Huawei Technologies

16. References [1] IEEE Std 802.11-2016 October 2017
Yanchun Li, Huawei Technologies

17. Appendix: Recap BTI+A-BFT for DMG AP with multiple antennas in 11ad
October 2017
Appendix: Recap BTI+A-BFT for DMG AP with multiple antennas in 11ad
An AP or PCP shall have an A-BFT every k beacon intervals (Fig.1);
The AP or PCP shall switch RX DMG antenna every l allocations (Fig. 2);
An AP or PCP with multiple DMG antennas has a regular schedule of receiving through each DMG antenna corresponding to the DMG antenna in which a DMG Beacon frame is transmitted through.
Fig.1, Low A-BFT density cases
Fig.2, Example for Antenna change
Yanchun Li, Huawei Technologies

18. Appendix: AP sends SSW feedback
October 2017
Appendix: AP sends SSW feedback
We consider feedback “the antenna IDs in the SSW feedback” in legacy way.
AP just feedback the antenna ID and report SNR in SSW feedback frame according to the SSW received by AP’s multiple Rx antennas.
AP may feedback according to received signal from only best one Rx antenna, depending on how AP will receive from this STA in future time. It is implementation dependent.
Yanchun Li, Huawei Technologies